Source : Webster's Revised Unabridged Dictionary (1913)

Colter \Col"ter\, n. [AS. culter, fr. L. culter plowshare,
   knife. Cf. {Cutlass}.]
   A knife or cutter, attached to the beam of a plow to cut the
   sward, in advance of the plowshare and moldboard. [Written
   also {coulter}.]

Source : WordNet®

colter
     n : a sharp steel wedge that precedes the plow and cuts
         vertically through the soil [syn: {coulter}]